Ulllted States Patent
`
`[19]
`
`|||||||l|||||||||||||||||||Illlllllllllllllllll||||l|||||||||||I|||||ll||||
`USOOS440613A
`[11] Patent Number:
`
`5,440,613
`
` .
`
`Fuentes
`
`[45] Date of Patent:
`
`Aug. 8, 1995
`
`
`
`[54] ARCHITECTURE FOR A CELLULAR
`WIRELESS TELECOMMUNICATION
`SYSTEM
`Inventor:
`
`[75]
`
`James J. Fuentes, South Barfington,
`In.
`
`International Mobile Machines
`System Description,
`Corporation, 1987, pp. 1.1—5.3.
`V. Breton et al., “Tangara: digital cordless telephone
`system”, Commutation Et Transmission, vol. 13, No. 3,
`1991, PariS, pp. 23—32.
`
`[73] Assignee: AT&T C01'p., Murray Hill, NJ.
`_
`[21] Appl' No" 281’249
`[22] Filed:
`Jul. 27, 1994
`
`Primmy Examiner—Curtis Kuntz
`Assistant Examiner—Dwayne D. Bost
`Attorney, Agent, or Firm—Werner Ulrich
`
`[57]
`
`ABSTRACT
`
`[63]
`
`R8111th US- Application Data
`Continuation of Ser. No. 998,310, Dec. 30, 1992, aban-
`cloned.
`51
`Int. Cl.6 ............................................... H04
`7 24
`iszi US. Cl. ........................................ 379/60- 39/59
`455/3332. 330/1101,
`[53] Field of Search ............................. 375/59, 60, 63;
`455/33.1, 333; 370/1101
`
`[56]
`
`References Clted
`U.S. PATENT DOCUMENTS
`4,245,538 12/1980 Ito et all
`.
`4,599,490 7/1935 Cornell e: at .
`4,811,380 3/1989 Spear ..................................... 379/60
`4,827,499
`5/1939 Warty 8t 81.
`-
`5,090,050 2/1992 Heffernan ........ n: .................. 379/60
`5,117,502 5/1992 Onoda et a1.
`......................... 379/60
`OTHER PUBLICATIONS
`Commutation & Transmission article, “PAN_European
`Digital Cellular System for Mobile Telephones”, Du-
`plessis et al., No. 2, 1986, pp. 5—14.
`Ultraphone 100 Wireless Digital Loop CarrierTM,
`
`This invention relates to a method and apparatus for
`offering wireless telecommunication service. A switch
`such as an automatic Private Branch Exchange (PBX),
`equipped to communicate With Integrated Services
`Digital Netw°rk (ISDN) Station sends ISDN Signaling
`messages to and receives ISDN signaling messages from
`a protocol converter- The protocol converter, which
`also communicates with a wireless cell site, converts
`messages between the ISDN protocol and a protocol
`for communicating with the wireless cell site. The cell
`site sets up wireless connections to a mobile station,
`essentially in its prior art mode, and the PBX sets up
`connections to the cell site essentially in its prior art
`ISDN station control mode. The system can also hand
`off calls from one cell site to another connected to the
`same PBX, using the protocol COHverter to generate
`and distribute the lecate request messages“ The system
`can further process roamers by allowing them to regis-
`ter locally and by directly connecting intra-system traf-
`fie to such roamers'
`
`10 Claims, 5 Drawing Sheets
`
`
`
`
`To OTHER
`47 cm SITES
`
`LINES 0R TRUNKS
`
`
`PUBUC SWITCHED
`TELEPHONE NETWORK
`
`
`
`
`YMAX EXHIBIT 1029
`
`YMAX CORP. V. FOCAL IP
`
`000001
`
`|PR2016-01260
`
`000001
`
`YMAX EXHIBIT 1029
`YMAX CORP. V. FOCAL IP
`IPR2016-01260
`
`

`

`US. Patent
`
`Aug. 8, 1995
`
`Sheet 1 of 5
`
`5,440,613
`
`
`
`RADIO
`CHANNEL
`
`2
`
`1 0
`
`CELL SITE
`
`
`
`VOICE I LAPB
`CHANNELS
`‘
`
`
`PROTOCOL
`CONVERTER
`
`
`]TO OTHER
`CELL SITES
`47
`
`UNES OR TRUNKS
`
`
`CENTRAL
`ome
`
`45
`
`46
`
`
`
`iii.
`_
`
`
`
`
`
`
`
`PUBUC SWITCHED
`
`TELEPHONE NETWORK
`
`
`
`FIG.
`
`1
`
`000002
`
`000002
`
`

`

`US. Patent
`
`Aug. 8, 1995
`
`Sheet 2 of 5
`
`5,440,613
`
`
`
`F3g:
`Q_‘m
`
`PC
`
`l
`
`MOBILE ORIGINATION
`I
`203 201
`
` DIRECTIONAL
`
`PC TRANSLATES
`
`ANTENNA IDENTITY
`
`INTO APPROPRIATE
`
`D—CHANNEL
`
`3%
`
`III I :
`
`:
`
`I I I I I I
`
`1
`
`PBX SELECTS
`B—CHANNEL
`I
`
`209
`
`1
`'
`:
`I
`
`:I
`
`I
`
`SETUP
`I
`206 205
`
`.
`
`CALL PROC
`2
`207
`
`RADIO NUMBER
`
`PC TRANSLATES
`B-CHANNEL INT0
`
`MOBILE SETUP
`
`I.
`
`:
`211
`'VOICE CHANNEL CONFIRMATION'
`k—j—i
`I
`21 3
`
`I
`
`PROGRESS
`
`215
`ALERT
`I
`219 217
`
`I .
`
`'
`I
`
`FAR END
`
`ANSWERS THE CALL
`
`CONNECT
`|
`I———T_——_.I
`221
`I
`PC RECORDS
`
`.
`
`223
`
`TALK STATE
`
`WIRELESS ORIGINATED CALL
`
`F]G. 2
`
`000003
`
`000003
`
`

`

`US. Patent
`
`Aug. 8, 1995
`
`Sheet 3 of 5
`
`5,440,613
`
`.0O
`
`PBX TRANSLATES
`DIRECTORY NUMBER
`INT0 APPROPRIATE
`D—CHANNEL
`
`PBX SELECTS
`
`B-CHANNEL ____.______._.___._|
` 4
`
`SEI'UP
`I
`307
`
`309
`
`PC TRANSLATES
`B-CHANNEL INTO
`RADIO NUMBER
`
`CALL PROC
`
`I
`
`
`
`I 3
`
`325
`I
`W :
`
`I
`
`329
`
`4
`
`PC RECORDS
`TALK STATE
`
`WIRELESS TERMINATED CALL
`
`FIG. 3
`
`000004
`
`CELL
`SITE
`
`I Ill ‘
`
`lI III II IIIlllI IIII Il| I II| |
`
`'
`I
`I
`I
`322
`'
`WIRELESS TERMINAL
`ANSWERS THE CALL
`
`II I
`
`I|l I |
`
`MOBILE PAGE
`I
`I
`I
`313
`PAGE RESPONSE
`I
`315
`MOBILE SETUP
`2
`319
`
`I I
`
`I
`'
`l
`I
`'
`I
`
`I I
`
`I
`ANSWER
`"—‘fifi
`I
`323
`
`311
`
`ALERT
`
`321
`
`CONNECT
`
`27
`
`000004
`
`

`

`US. Patent
`
`Aug. 8, 1995
`
`Sheet 4 of 5
`
`5,440,613
`
`PC 20
`
`E
`
`P
`
`8
`
`CELL SITE 9
`I888—8000I
`
`CELL SITE 10
`I777—7000I
`
`
`
`
`STABLE CALL
`ON CELL #1
`
`
`713—1 100
`
`SIGNAL <
`THRESHOLD
`
`LOCATE
`REQUEST
`
`"I
`I
`LOCATE
`I
`RESPONSE
`I
`(ONLY >
`THRESHOLD
`CAUSES
`_ RESPONSE)
`
`lIII|||
`
`LOCATE
`
`REQUEST
`
`RLE‘IIIIAIISET
`
`LOCATE
`
`
`
`HANDOFF
`COMMAND
`I
`
`I
`
`I
`
`IIIII|III I
`
`I
`I
`I
`
`IIIIIIIIIlIIII
`
`REQUEST
`
`402 I
`I
`I PC ROUTES TO I
`I ALL NEIGHBORS I
`I
`REngéIIEE
`I
`LOCATE
`I
`I
`RESPONSE H——-——1
`‘-——|
`PC SELECTS
`I
`HAND-OFF CELL 2
`I
`ISETTIP CALL TRANsI
`' ARRANGEMENT
`I
`'
`TRANS
`I
`I
`(TRANSFER TO
`I
`I
`888—8000)
`'
`I
`HOLD ACK
`p——__—____4
`I
`(713-1100
`I
`ON HOLD)
`I
`SETUP
`L——>I
`SETUP
`—————-———>
`_
`I
`
`HAND-OFF
`REQUEST
`
`(713-1100)
`MOBILE
`ON CHANNEL
`
`I
`I
`I
`
`IIIlII
`
`FROM
`713—1100)
`CONNECT
`
`—_———_————_a._——_—
`
`I I
`
`|
`'
`CONNECT
`I
`p————————A
`,
`(888—8000)
`|
`I
`TRANSFER
`I
`I
`(713-1100)
`I
`TRANSFER ACK I
`
`I I
`
`I
`DISCONNECT
`p—————————4
`I
`RELEASE
`I
`I
`RELEASE
`'|
`I
`COMPLETE
`|
`
`000005
`
`000005
`
`

`

`US. Patent
`
`Aug. 8, 1995
`
`Sheet 5 of 5
`
`5,440,613
`
`CELL SITE 10
`(777—7000!
`
`PC
`D—CHANNEL
`
`flSlN
`
`I
`
`:l
`
`,
`
`CALL FORWARDINC REQUEST
`(FOR (700)979-5400
`To 777—7000)
`SETUP T0 777—7000
`ECALL FORWARDED FROM
`7oo)979—54oo ON 88)
`
`|
`AUTO REGISTRATION
`|
`T———-——-—-———-1
`(MOBILE N0. 0R (700)979-5400 I
`FOR DIALING PLANS THROUGHOUT
`NETWORK)
`
`
`
`I
`'
`
`PAGE
`(MOBILE (700)979-5400)
`
`PAGE RESPONSE
`
`|| ll l l
`
`I| :
`
`l1
`
`ALERT
`
`|
`I
`I
`:1
`SETUP
`:
`:
`W CONNECT
`W :
`;
`(0N CHANNEL 8)
`I
`CONNECT ACKNOWLEDGE
`'
`k—-————-—-——l
`I
`I
`
`R AMING
`
`FIG. 5
`
`000006
`
`000006
`
`

`

`1
`
`5,440,613
`
`2
`and make calls within and outside the cellular communi-
`
`ARCHITECTURE FOR A CELLULAR WIRELESS
`TELECOMNIUNICATION SYSTEM
`
`This application is a continuation of application Ser.
`No. 07/998,310, filed on Dec. 30, 1992, abandoned.
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application relates to an application by James J.
`Fuentes entitled “Architecture For A Wireless Tele-
`communication System”, filed Aug. 11, 1992, Ser. No.
`928,386, and assigned to the same assignee as this appli-
`cation.
`
`TECHNICAL FIELD
`
`5
`
`10
`
`15
`
`This invention relates to wireless telecommunication
`
`systems and, more specifically, to architecture for small
`growable cellular wireless
`telecommunication net-
`works.
`
`20
`
`
`
`PROBLEM
`
`Wireless telecommunication networks have grown
`very rapidly in the past decade as a result of substantial
`breakthroughs in the cost of wireless telecommunica-
`tion terminals, otherwise known as mobile stations.
`Such mobile stations exist in many forms from those
`which are mounted in automobiles to portable stations
`to hand held stations. The cellular principle has permit-
`ted a large growth in the amount of wireless telecom-
`munications which can be carded over the allooated
`radio spectrum thus allowing a huge growth in the
`number of wireless telecommunication subscribers.
`
`While major cost breakthroughs have taken place in
`the customer equipment (the radio transceivers for
`communicating with the cellular systems), a similar cost
`breakthrough has not taken place in the central office
`equipment required to establish connections between
`customer stations. In particular, while large systems
`have been designed whose per subscriber cost is not
`high, a small and inexpensive but growable small wire-
`less cellular switching system is not available in the
`prior art. Such a system is particularly desirable for use
`in low density cellular areas such as a remote service
`area.
`
`SOLUTION
`
`The above problem is solved in accordance with this
`invention wherein a moderate size switching system,
`such as a midsize private branch exchange (PBX) is
`used as the mobile telecommunication switching office;
`in a departure from the prior art, this system is adapted
`for use in the cellular application by virtue of an archi-
`tecture which allows the PBX to communicate with the
`cell sites of the cellular system as if these cell sites were
`other PBXs communicating, via a system using out of
`band signaling, referred to hereinafter as out of band
`telephone station control (OTSC), such as that used in
`integrated services digital network (ISDN) communica-
`tion links, wherein the out of band signaling communi-
`cates with a protocol converter to convert between
`ISDN and cell site protocols. In accordance with this
`invention, the system is equipped for autonomous regis-
`tration and for handoff so that customers can move
`within one cell from areas covered by one directional
`antenna to areas covered by another directional antenna
`and can move from cell to cell. In one embodiment,
`outside customers (roamers) can autonomously register
`
`cation system and receive calls from outside that sys-
`tem. In one embodiment, the cell sites, which are exist-
`ing prior an cell sites, receive data communications
`from a protocol converter inserted in the data link part
`of the ISDN connection; the protocol converter con-
`verts signals from the PBX from ISDN protocol to a
`protocol accepted by the cell site and converts cell site
`data messages in a protocol normally destined for a
`mobile switch from the cell site protocol to an ISDN
`protocol. Advantageously, such an arrangement per-
`mits the PBX to set up cellular connections in essen-
`tially the same way that the PBX is already equipped to
`set up ISDN connections.
`In one specific embodiment of the invention, a pri-
`mary rate interface (PR1) carrying a plurality of B-
`channels and one D-channel is used to connect the PBX
`with a cell site; the protocol converter in this case con-
`verts messages on the D-channel. A plurality of primary
`rate interfaces may share a single D-channel on one of
`these interfaces. Advantageously,
`the protocol con-
`verter need only communicate with a small number of
`data channels. Advantageously, the development effort
`is minimized because existing PBXs, cell sites, and
`ISDN and cell site protocols are used, so that only
`software for the protocol converter needs to be devel-
`oped.
`'
`In one embodiment, the PBX is connected to other
`PBXs by primary rate interface connections. This per-
`mits connections to be set up between stations served by
`two different PBXs connected by such a primary rate
`interface. In one specific embodiment of the invention,
`the PBX is a System 75 Definity ® PBX which is manu-
`factured by AT&T. Such a system is adapted to inter-
`face with other PBXs via primary rate interface ISDN
`communication links. Advantageously, the use of such a
`system avoids the need for reprogramming a PBX to
`accomplish the objectives of the invention.
`In accordance with another specific embodiment of
`applicant’s invention, land-based customer lines are also
`connectable to the PBX. Advantageously, the PBX can
`then serve both land-based and mobile stations.
`
`Growth for such a system is straightforward. First,
`the capacity of the cell site is increased to its maximum.
`Then, additional cell sites are added under the control
`of one PBX. Then, another PBX may be added, along
`with its cell sites. Finally, an Autoplex ® 1000 system
`such as that described in US. Pat. No. 4,827,499 can be
`formed by adding a control processing complex to con-
`trol~ the PBXs and the cell sites, or the PBXs may be
`replaced by a mobile communications telecommunica-
`tion switch which can communicate directly with the
`cell sites without using a protocol converter.
`BRIEF DESCRIPTION OF THE DRAWING
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55‘
`
`FIG. 1 is a block diagram illustrating the operation of
`the invention;
`FIGS. 2 and 3 are flow and message diagrams illus-
`trating the steps of establishing an incoming and an
`outgoing call;
`FIG. 4 is a flow and message diagram of a hand-off
`process; and
`FIG. Sis a flow and message diagram of treatment of
`a roamer.
`
`65
`
`DETAILED DESCRIPTION
`
`FIG. 1 is a block diagram illustrating the operation of
`applicant’s invention. A radio cell site 10 communicates
`
`000007
`
`
`
`000007
`
`

`

`
`
`5,440,613
`
`3
`via radio channel 2 with a mobile station 1. A cell site
`
`such as the Autoplex ® Series I Mod II Cell Site can be
`used in this application. A different cell site can be used
`if the European Global Systems for Mobile Communi-
`cations (GSM) standard protocol is required. The cell
`site is connected by a multiplexer 35 to one or more
`primary rate interface integrated services digital net-
`work (PRI-ISDN) communication channels 31, 32, 33
`to a private branch exchange (PBX) 30. The multiplexer
`35 strips the D-channel from the PRI signals and sends
`these D-channel signals via data link 38 to protocol
`converter 20 connected via data link 39 to cell site 10. A
`multiplexer such as the Crossnet 442 multiplexer manu-
`factured by Tellabs can be used. A NCR 3330 (Intel 486
`based) computer manufactured by NCR Inc. can be
`used as the protocol converter (PC); the NCR com-
`puter is equipped with an interface board such as a
`DLPI/HDLC Controller Board for UNIX ® systems
`to terminate the two data links to the PC. Cell site 10
`receives its control signals over the data link 39 and
`transmits its responses and its own initiated data mes-
`sages over that link. The protocol converter converts
`between ISDN control messages
`specified in the
`CCITT Q.93l call control message set and the message
`set required to interface with a cell site. This message
`set may be proprietary or it may conform with a stan-
`dard such as that specified in the European GSM stan-
`dard for wireless communications.
`PBX 30 is also connected by lines such as line 42 to
`land based telephone stations such as station 48; by one
`or more PR1 facilities 41 to one or more other PBXs 44,
`the latter being for connection to the other cell sites; by
`one or more PRI facilities 47 to one or more other cell
`sites connected to PBX 30; and by facilities such as lines
`or trunks 43 to a class 5 central office switch 45, the
`latter being for connection to to a public switched tele-
`phone network for accessing of telephones and mobile
`stations outside the immediate region covered by PBXs
`30 and 44 and central office 45. The connection to the
`class 5 central office can be over line facilities, one or
`more PRI facilities, or even T-carrier trunk facilities; a
`line interface is the most natural for communicating
`between a PBX and a central office, especially an older
`central office, and simplifies the process of billing at the
`central office.
`The PBX keeps track of the busy-idle state of all
`mobile stations currently associated with a cell site.
`When a disconnect is received, the B-channel is made
`available through a release message from the PC; this
`makes the B-channel, and its associated radio channel,
`available, and changes the busy-idle state of the mobile
`station to idle.
`
`FIG. 2 illustrates the messages and the actions per-
`formed by the protocol converter 20 in setting up a
`wireless originated call. The cell site 10 receives an
`indication from the mobile station 1 that the mobile
`station wishes to originate and receives the number of
`the called customer dialed by the originating mobile
`station. Cell site 10 sends message 201 to PC 20, the
`message containing an identification of the calling main
`station, the called number, and an indication of which
`directional antenna is optimum for use on this call. The
`mobile station picks the set-up channel that corresponds
`to the optimum directional antenna. The protocol con—
`verter 20 translates the directional antenna identity into
`the appropriate D-channel 39 for use in communicating
`with the PBX 30. If one D-channel serves all of the
`PRIs connecting the PBX to the cell site, this transla-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`4
`tion is not required. The PC then transmits a set-up
`message 205, including the called directory number and
`an identity of the caller, to PBX 30. As shown in action
`box 206 PBX 30 then selects a B-channel appropriate
`for use with the identified directional antenna and trans-
`mits over D—channel 38 a call proceed message 207
`identifying the selected B—channel. In action block 209,
`PC 20 translates the B-channel identity into a radio
`number and transmits a mobile set-up message 211 to
`the cell site to establish communication between the
`selected B-channel and the mobile station 1. The cell
`site 10 having confirmed the establishment of such a
`radio communication then returns to the protocol con—
`verter 20 a voice channel confirmation message 213.
`In the meantime, PBX 30 has been establishing the
`other end of the connection and transmits a series of call
`
`progress messages 215 to PC 20 which maintains track
`of the status of the connection. When the connection
`
`has been established, an alert message 217 is sent from
`PBX 30 to PC 20 indicating that the called customer is
`being alerted. The calling customer hears audible tone.
`The PBX 30 then detects that the call has been an—
`swered (action block 219) and transmits a connect mes-
`sage 221 to the PC 20. In response, the PC 20 records
`that the connection is now in the talk state (action block
`223).
`FIG. 3 illustrates a wireless terminated call. Action
`block 301 indicates that the PBX has received an incom-
`ing or an originating call. The PBX translates the direc—
`tory number into the appropriate D-channel for use in
`communicating with the protocol converter (action
`block 303). The PBX then selects a B-channel to be used
`for this conversation (action block 305). In this embodi-
`ment, each PRI can serve only one cell site sector, but
`several PRIs may serve one sector. The PBX then sends
`a set-up message including the identity of the called
`main station and the identity of the B-channel to be used
`for the connection (message 307). The PC 20 translates
`this B-channel number into a radio number (action
`block 309) and transmits,
`in response, a call process
`proceeding message 311 back to the PBX. The PC 20
`then transmits a request to page the mobile via message
`313 transmitted over data channel 39 to cell site 10. Cell
`site 10 pages the mobile and if the mobile responds
`properly, transmits a page response message 315 back to
`PC 20. The PC then sends a mobile set-up message 319
`to the cell site requesting that the connection between
`the selected B-channel and the mobile station be estab-
`lished and that that connection be monitored to deter-
`mine whether the called mobile station answers the call.
`The PC also sends an alert message back to the PBX to
`indicate that the calling party should receive audible
`ringing tone. When the wireless terminal answers the
`call (action block 322) an answer message 323 is sent
`from the cell site to the PC. The PC passes on a connect
`message 325 to request that the PBX complete the con-
`nection to the called customer and remove the audible
`
`ringing tone connection. After completing this task, the
`PBX returns a connect acknowledge message 327 to the
`PC and the PC records the talking state for that connec-
`tion (action block 329).
`Usually, the PBX is connected to a class 5 central
`office (end office) or to a tandem or toll switching sys—
`tem in order to allow the wireless customers to access
`
`the public switched telephone network. By connecting
`the PBX to a class 5 central office, it is possible to han—
`dle the roaming problem in a very straightforward way.
`If a roamer enters the area covered by the cell site of the
`
`
`
`000008
`
`000008
`
`

`

`
`
`5,440,613
`
`5
`exemplary system, and turns on its radio in order to
`perform the registration function, well known in the
`prior art, the cell site transmits information concerning
`the roamer to a PBX which forwards it to a central
`office. Additionally, registration can be performed peri-
`odically after an initial registration on mobile power
`tum-on. The central office then initializes the PBX to be
`
`able to accept calls from that roamer and notifies a
`larger wireless systems network of the location of the
`roamer. Calls are then forwarded from a home switch-
`
`10
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`ing system to the serving cell site, each cell site being
`identified by a directory number. Calls to parties not
`connected to the PBX via either a radio channel or a
`direct connection are handled by connections from the
`PBX to the controlling central office. The latter can
`then establish a connection over public switched tele-
`phone network to any destination. Incoming calls can
`similarly be handled by terminating such calls to the
`connected central office and completing the connection
`through a connection to the PBX which makes a con-
`nection to a line connected to the PBX directly or via a
`radio channel.
`The central office can be connected to the PBX using
`any of the standard central office PBX transmission and
`signaling facilities. The use of a common channel signal-
`ing arrangement between the PBX and the central of-
`fice enhances the flexibility of the system.
`FIG. 4 is a diagram illustrating the process of handing
`off wireless communication from one cell site to an-
`other. Each directional antenna of each cell site has a
`directory number. In this case we will illustrate the
`handoff from the selected antenna of cell site 10 to the
`selected antenna of cell site 9. Cell site 10 or, if appropri-
`ate,
`its directional antenna, has directory number
`777-7000 while cell site 9, or, if appropriate, its direc-
`tional antenna, has directory number 888-8000. The
`mobile phone has a directory number 713-1100. Cell site
`10 recognizes that the strength of the radio signal from
`mobile 713—1100 (i.e., mobile 1) has drOpped below an
`upper threshold suggesting that a handoff is desirable.
`Cell site 10 sends a message to neighboring cell sites
`requesting a signal strength measurement for the speci-
`fied mobile unit. This message, a locate message, identi-
`fies the radio channel on which the mobile station 1 is
`currently transmitting.
`In this preferred embodiment, the locate message is
`sent to protocol converter 20 as a conventional mobile
`radio locate message. Protocol converter 20 sends an
`X.25 message to protocol converters associated with
`each of the neighboring cell sites (action block 402).
`The pertinent protocol converter associated with cell
`site 9, Le, PC8, receives this message and sends the
`locate request to cell site 9. In this preferred embodi-
`ment,
`the broadcast capability offered by AT&T’s
`ISDN PRI implementation for X.25 message routing is
`used to generate multiple sessions for transmitting the
`locate request message to multiple destinations. The
`multiple sessions are used to generate the multiple mes-
`sages to neighboring cell sites. This arrangement, in
`effect, provides the packet switching required to send
`messages to all neighboring cell sites.
`The locate request messages are distributed as fol-
`lows. Each protocol converter is connected via an X.25
`permanent virtual circuit to all neighbor cells which are
`potential targets for handover. This facility can easily
`be implemented using, for example, an AT&T Uniprism
`card as part of the protocol converter. The cell site
`signals its connected protocol converter via its LAPB
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`connection (connection 39 for cell site 10). This LAPB
`message is used by the protocol converter to generate
`ISDN messages to each of its neighbor cell sites using
`the X.25 permanent virtual circuits and transmitted
`over one or more ISDN D-channel links.
`
`Cell site 9 performs the signal strength measurement
`and sends back a locate response message to its protocol
`converter, PC8, which forwards this locate response
`message to the protocol converter 20. Protocol con-
`verter 20 receives the measurements from all neighbor-
`ing cells receiving above threshold signals and selects a
`cell site which has adequate signal strength.
`The final steps of hand~off are performed in accor-
`dance with the principles of any conventional hand-off
`procedure, taking into account the use of the protocol
`converters, PC 8 and PC 20 to convert between the
`messages generated or received by the cell sites and the
`messages generated or received by the PBX or other
`switching system. In this embodiment, these steps are as
`indicated in the balance of FIG. 4. Assume, in this case,
`that the cell site selected for hand-off is cell site 9. Pro-
`tocol converter 20 sends a request message to PBX 30 to
`set up a call transfer arrangement between the specified
`B—channel on which mobile 1 is presently communicat-
`ing, and a B-channel of the primary rate interface to cell
`site 9 identified by directory number 888-8000. The call
`transfer arrangement permits a subsequent new connec-
`tion to cell site 9 to be made rapidly as soon as the
`mobile radio has been retuned; such a connection can be
`readily established using a time division switch. The
`PBX selects a B-channel (in this case, B-channel 501) in
`the primary rate interface to cell site 9 and sends a set-
`up message to cell site 9 via its associated protocol
`converter. Protocol converter 8 transmits a hand-off
`request message to cell site 9 requesting that mobile
`station 1 (identified by directory number 713-1100)
`currently transmitting on B-channel 500 is to be trans-
`ferred to a channel of a PRI for accessing the directory
`number associated with cell site 9. PC 20 sends a set up
`request to set up to a specific channel 501 of cell site 9.
`The set—up request is converted by PC 8 to a hand-off
`request to channel 501. Responsive to an acknowledg-
`ment of the hand-off request (not shown), PC 20 sends
`a hand—off command to cell site 10 to cause mobile
`
`station 1 to retune to channel 501. Cell site 9 responds
`with a confirmation message identifying the mobile and
`the new channel number (assumed in this case to be
`channel 501 ) as soon as the mobile has been retuned and
`the mobile signal is detected on the new channel. As
`soon as retuning has been successfully accomplished, an
`on—hook message is sent from cell 10 with respect to
`PRI channel B1 to protocol converter 20 and this on-
`hook message is passed on to PBX 30. PBX 30 then
`changes the call transfer arrangement to route the call
`to cell site 9.
`Alternatively, a conference connection can be used
`wherein both cell site 9 and cell site 10 are simulta-
`neously connected to the other party; this allows for a
`smoother transition, but is more expensive.
`While in this particular implementation a PBX is used
`for controlling the handoffs, in other implementations a
`central office, such as central office 45, can be used.
`Note further that another PBX, such as PBX 44, can be
`connected to PBX 30 through one or more primary rate
`interfaces and PBX 44 can be connected to target hand-
`over cell sites. In this case, messages between protocol
`converters and their associated PBXs must also be
`passed to the other PBX for transmission to their associ-
`
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`ated protocol converters whenever a target cell site is
`connected to another PBX.
`
`In order to ensure that the proper party is billed for
`transferred calls, reverse charging is used on all trans-
`ferred calls to associate the charge with the directory
`number of the mobile station and not the directory
`number of the handoff cell site.
`FIG. 5 illustrates the process of registering roamers
`and handling calls for such mobile units. In this particu-
`lar case,
`the roamer has a directory number of
`700-979—5400. The 700 identifies the mobile station as a
`roamer. When a registration request is originally re-
`ceived from a mobile station (this happens when the
`mobile station turns on its power) an auto registration
`request is passed from cell site 10 to its associated proto-
`col converter 20. The protocol converter checks
`whether the mobile is already registered in that cell site
`and if not, sends a message to PBX 30 that all calls for
`700-979-5400 should be forwarded to 777-7000,
`the
`directory number of cell site 10. In addition, the PBX
`checks to see if 700-979-5400 is on its roamer list and if
`not, sends a message to a centralized 700 data base to
`verify that roamer 700-979-5400 is a valid roamer num—
`ber to which service may be provided at this time and to
`inform a centralized 700 data base of the present loca-
`tion (the directory number of the cell site) of the
`roamer. PBX 30 sends a validation message to protocol
`converter 20 in response to which protocol converter
`registers the mobile. The validation message includes
`the serial number of the mobile.
`In response to an incoming call from the public
`switched telephone network, the call having been for-
`warded with the aid of the 700 data base, such a call is
`received in the PBX 30. PBX 30 sends a set-up message
`to cell site 10 (directory number 777-7000) to forward
`the call for 700-979-5400 and identifies the B-channel
`being used for that message as B—channel 8. Protocol
`converter 20 sends a page request message to cell site 10
`to page mobile 700-979-5400. The serial number of the
`mobile station (which was previously recorded in re-
`sponse to the registration) is sent as part of the page
`message. The page response is returned to protocol
`converter 20 which sends an alert message to PBX 30 to
`cause the PBX to return audible tone to the caller, and
`a set-up message for mobile 700-979-5400 to cell site 10.
`When the mobile answers, an answer message is sent
`from the cell site to the protocol converter 20 which
`transmits a connect message to PBX 30 which com-
`pletes the connection and sends a connect acknowledge
`message back to protocol converter 20.
`The public switched telephone network forwards
`outside calls to the roamer by consulting the centralized
`700 data base, used for roamers and customers having
`“Follow Me” service, whenever there is a call to that
`roamer. Calls from the public switched network are
`then simply forwarded to the roamer. Calls from one of
`the cell sites served by the PBX are directly connected
`to the roamer, since the roamer has been registered in
`that PBX.
`
`Growth for such a system is straightforward. First,
`the capacity of the cell site is increased to its maximum.
`Then, additional cell sites are added under the control
`of one PBX. Then, another PBX may be added, along
`with its cell sites. Finally, an Autoplex 1000 system such
`as that described in US. Pat. No. 4,827,499 can be
`formed by adding a control processing complex to con-
`trol the PBXs and the cell sites, or the PBXs may be
`replaced by a mobile communications telecommunica-
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`tion switch which can communicate directly with the
`cell sites without using a protocol converter.
`An advantage of this system is the relatively simple
`functionality required at the PBX. As it becomes easier
`to provide advanced functionality at the PBX, this PBX
`can be enhanced to control handoffs using essentially
`the same methods that are already well known in the
`prior art.
`This particular embodiment has illustrated ISDN
`protocol and an ISDN PRI interface to the PBX. The
`advantage is that the PBX can then interface with the
`PC and the cell site as if these were ordinary connec-
`tions to the PBX. Any other arrangement which allows
`out of band signaling for controlling telephone stations
`to be conveniently terminated on the PBX would also
`meet this requirement.
`It is to be understood that the above description is
`only of one preferred embodiment of the invention.
`Numerous other arrangements may be devised by one
`skilled in the art without departing from the scope of
`the invention. The invention is thus limited only as
`defined in the accompanying claims.
`I claim:
`
`1. A wireless telecommunications system for handing
`off calls from one to another of a plurality of cell sites,
`comprising:
`-
`a telecommunications switching system convention-
`ally adapted to communicate only with land based
`stations and land based switching systems;
`a plurality of wireless cell sites arranged for commu-
`nicating with a mobile switching center;
`protocol conversion means for converting between a
`cell site control protocol, said cell site control pro-
`tocol for signaling to and receiving signals from a
`wireless cell site, and an out of band telephone
`station control (OTSC) protocol for communicat-
`ing between a telecommunications switching sys-
`tem and a land based telephone station;
`wherein said telecommunications switching system is
`connected to each of said plurality of wireless cell
`sites by a plurality of communication links, and said
`telecommunications switching system is connected
`to each of said plurality of wireless cell sites by data
`link means via said protocol conversion means;
`wherein said telecommunications switching system
`sends OTSC protocol signaling messages of